Breast cancer is the most common malignancy among women in the United States, with an estimated 178,480 cases and 40,460 deaths from breast cancer among women projected for 2007. Epidemiological and laboratory evidence indicates that vitamin D may be protective against breast cancer incidence;however, no large studies have addressed the association between vitamin D and breast cancer recurrence. We hypothesize that serum concentrations of 25(OH)D are inversely associated with breast cancer recurrence, and that this relationship will be stronger than that for dietary or supplemental intake of vitamin D and recurrence. Vitamin D holds significant potential as a preventive approach to reduce tertiary disease in that there is no toxicity related to usual exposure, and increases in dietary and/or supplemental vitamin D could be easily adopted in a cost-efficient manner by the over 2 million breast cancer survivors in the United States today. The Women's Healthy Eating and Living (WHEL) Study, a large dietary intervention trial of the effectiveness of a high-vegetable, low-fat diet in reducing breast cancer recurrence, provides the framework for conducting such a study in an efficient manner. Therefore, within the WHEL Study and using a nested case-control design, the specific aims of the proposed work are to 1) Measure circulating 25(OH)D levels in women in the WHEL cohort at baseline and evaluate the association between serum 25(OH)D and breast cancer recurrence;2) Evaluate the association between dietary and supplemental intake of vitamin D and breast cancer recurrence;3) Explore whether calcium, vitamin A, carotenoids, or body size, modify the association between 25(OH)D and breast cancer recurrence using serum concentrations and dietary intake data. Two secondary aims are: 1) To explore whether the association between serum 25(OH)D, intake of vitamin D, and breast cancer recurrence vary by tumor estrogen- receptor status or menopausal status and 2) To create a predictive model of circulating 25(OH)D levels based on data for supplemental and dietary vitamin D intake, race, season, and body size. The work proposed herein has the potential to have immediate, low-cost impact on breast cancer survival recurrence. PUBLIC HEALTH RELEVANCE: Vitamin D holds significant potential as a preventive approach to reduce tertiary disease in that there is no toxicity related to usual exposure, and increases in dietary and/or supplemental vitamin D could be easily adopted in a cost-efficient manner by the over 2 million breast cancer survivors in the United States today. In the proposed work, we hypothesize that serum concentrations of 25(OH)D are inversely associated with breast cancer recurrence, and that this relationship will be stronger than that for dietary or supplemental intake of vitamin D and recurrence.